The present invention relates to a power conversion apparatus such as an uninterruptible power supply that is capable of supplying power to a load even if an abnormality, such as a power failure or a momentary voltage drop, occurs in a system power supply. More particularly, the present invention relates to an apparatus having a function of coping with unbalanced loads.
A conventional AC/DC conversion apparatus disclosed in JP Patent No. 2765372 is shown in FIG. 24. In this drawing, reference numeral 100 denotes an AC power supply, numeral 101 a switch means, numeral 102 a reactor, numerals 103 and 104 transistors, numerals 105 and 106 diodes, numerals 107 and 108 capacitors, numerals 109 and 110 resistors functioning as DC loads, and numeral 111 a battery.
In the apparatus constructed in this manner, in the case where the AC power supply 100 operates normally, the switch means 101 is connected to a contact point A and the transistors 103 and 104 are alternately turned on/off. As a result, a current of the reactor 102 is controlled so that the power factor of a current flowing to the AC power supply 100 becomes one, and the capacitors 107 and 108 are charged. Also, the charged energy is supplied to each of the resistors 109 and 110.
Also, in the case where an abnormality, such as a power failure, occurs in the AC power supply 100, energy is supplied from the battery 111 to the resistors 109 and 110. During this operation, in the case where the resistors 109 and 110 have the same resistance value, that is, in the case where these resistors consume the same amount of power, the amount of energy supplied from the capacitor 107 to the resistor 109 becomes the same as that supplied from the capacitor 108 to the resistor 110. As a result, the voltages of the capacitors 107 and 108 become equal to each other at all times. That is, the voltage values of the capacitors 107 and 108 are balanced by the energy supplied from the battery 111.
However, in the case of unbalanced loads where values of the resistors 107 and 108 differ from each other, for instance, voltages values of the capacitors 107 and 108 are unbalanced. This is because only the battery 111 charges the two capacitors 107 and 108 and it becomes impossible to control the potential at an interconnection point C between the capacitors 107 and 108.
Even if the AC power supply operates normally, in the case of such unbalanced loads, an imbalance occurs. However, for instance, JP Laid-Open No. 2000-278954 discloses a technique of eliminating imbalance by changing the ratio between on/off times during the switching of the transistors 103 and 104 using an unillustrated control circuit.
By the way, if an abnormality like a power failure occurs in the AC power supply 100 and the voltages of the capacitors 107 and 108 are unbalanced, there occurs a problem that desired voltages are not applied to the loads 109 and 110. That is, in the case of unbalanced loads where the value of the resistor 110 is smaller than the value of the resistor 109, for instance, the voltage of the capacitor 108 ultimately becomes zero and the voltage of the capacitor 107 becomes VB.
In view of this problem, with the conventional technique disclosed in the above-mentioned publication, in the case where an abnormality like a power failure occurs in the AC power supply 100, the switch means 101 is switched to a contact point B. Also, to stabilize the potential at the interconnection point C, the current of the reactor 102 is controlled by performing the switching of the transistors 103 and 104 using an unillustrated control circuit. As a result of this operation, the voltages of the two capacitors 107 and 108 become equal to each other at all times even in the case of the unbalanced loads. Also, power supply to the loads 109 and 110 is performed with stability.
By the way, in the case of a single-phase three-wire system AC power supply, conversion blocks 114 and 115, each of which includes a reactor, a transistor, and a diode a in FIG. 24, are connected to AC power supplies 112 and 113, as shown in FIG. 25. In this drawing, reference numerals 116 and 117 denote capacitors, numerals 120 and 121 resistances, and numeral 124 a battery.
In the case of such a single-phase three-wire system, an attempt may be made to use the conventional technique disclosed in JP Patent No. 2765372 described above, which is also capable of coping with unbalanced loads when an abnormality occurs in an AC power supply. Then, there may be conceived a method with which control is performed so that the voltage values of the capacitors 116 and 117 are balanced by switching contact points of the switch means 125 and 126 as shown in FIG. 26. However, with the construction shown in FIG. 26, the voltages VC1 and VC2 of the capacitors 116 and 117 are applied to the reactors within the conversion blocks 114 and 115 as they are, so that there occurs a problem that ripple currents flowing to the reactors become large. As a result, the efficiency of AC/DC conversion is lowered or noise from the reactors is increased.
Also, as shown in FIG. 27, there may be a case where a filter capacitor 130 is connected to remove a ripple current that occurs in the reactor 102 due to the switching of the transistors 103 and 104. In this case, as shown in FIG. 28, when it is detected that an abnormality occurs in the AC power supply 100 (T(fault)) and the switch means 101 is switched from xe2x80x9cAxe2x80x9d to xe2x80x9cBxe2x80x9d, a voltage remains in the filter capacitor 130. Consequently, a steep current that leads to the discharging of the voltage of the filter capacitor 130 is generated concurrently with the switching of the switch means 101. Also, this steep current flows to the switch means 101, so that there may occur a problem that the switch means 101 is damaged by an excess current. FIG. 28(a) shows a voltage waveform of the AC power supply 100, FIG. 28(b) shows a voltage waveform of the filter capacitor 130, and FIG. 28(c) shows a current waveform of the filter capacitor 130.
The present invention has been made to solve the problems described above, and a first object of the present invention is to provide a power conversion apparatus having a plurality of AC power supplies, wherein even if an abnormality occurs in at least one of the AC power supplies and loads that are respectively connected to two capacitors are not balanced, the power conversion apparatus is capable of balancing voltages of the two capacitors and is also capable of reducing losses and noises by decreasing a ripple current flowing to a reactor during the switching of the transistors 103 and 104.
Also, in the case where a filter capacitor is connected, a second object of the present invention is to provide a power conversion apparatus that is capable of preventing a situation where a switch means is damaged because electric charges of the filter capacitor are discharged and a steep current flows to the switch means when the switch means is turned on.
Further, in the case where a filter capacitor is connected, a third object of the present invention is to provide a power conversion apparatus that is capable of reducing losses by suppressing unnecessary resonance that occurs between the filter capacitor and a reactor when a switch means is turned on.
According to the present invention, a first power conversion apparatus is provided with: a first AC/DC conversion means constructed by connecting a first AC power supply, a first reactor, and a series body of a first switching means in series; a second AC/DC conversion means constructed by connecting a second AC power supply, a second reactor, and a series body of a second switching means in series; two capacitors connected in series, an interconnection point of the two capacitors being connected to one end of each of the two AC power supplies, and the two capacitors receiving energy supplied by DC voltages obtained by the first and second AC/DC conversion means; loads that are respectively connected to the two capacitors; and a battery connected to the two capacitors that are connected in series,
the power conversion apparatus comprising:
a first switch means that is connected between the first AC power supply and the first reactor, connects the first reactor to the first AC power supply if the first and second AC power supplies operate normally, and connects the first reactor to a connection point between the second reactor and the series body of the second switching means if one of the first and second AC power supplies operates abnormally;
a second switch means that is connected between the second AC power supply and the second reactor, connects the second reactor to the second AC power supply if the first and second AC power supplies operate normally, and connects the first reactor and the second reactor in series by connecting the second reactor to an interconnection point between the capacitors if one of the first and second AC power supplies operates abnormally; and
a control apparatus that controls a voltage difference between the two capacitors, wherein:
if the first and second AC power supplies operate normally, the control apparatus controls a current flowing to the first reactor using the series body of the first switching means to perform AC/DC conversion and controls a current flowing to the second reactor using the series body of the second switching means to perform AC/DC conversion; and
if one of the first and second AC power supplies operates abnormally, the control apparatus has the battery supply energy to the two capacitors and controls the current flowing to the first reactor using the series body of the first switching means.
With this construction, in the power conversion apparatus having the plurality of AC power supplies, when at least one of the AC power supplies operates abnormally, even in the case where loads that are respectively connected to two capacitors are unbalanced, it is possible to balance voltages of these capacitors. Also, during this operation, there is obtained an effect that losses and noises are reduced by reducing ripple currents flowing to the reactors due to the opening/closing of the first switching means.
According to the present invention, a second power conversion apparatus is provided with: a first AC/DC conversion means constructed by connecting a first AC power supply, a first reactor, and a series body of a first switching means in series; a second AC/DC conversion means constructed by connecting a second AC power supply, a second reactor, and a series body of a second switching means in series; two capacitors connected in series, an interconnection point of the two capacitors being connected to one end of each of the two AC power supplies, and the two capacitors receiving energy supplied by DC voltages obtained by the first and second AC/DC conversion means; loads that are respectively connected to the two capacitors; and a battery connected to the two capacitors that are connected in series,
the power conversion apparatus comprising:
a first switch means that is connected between the first AC power supply and the first reactor;
a second switch means that is connected between the second AC power supply and the second reactor;
a third switch means that is connected between a connection point between the first switch means and the first reactor, and a connection point between the second reactor and the series body of the second switching means;
a fourth switch means that is connected between a connection point between the second switch means and the second reactor, and an interconnection point between the capacitors;
a series body of a fifth switch means and a first filter capacitor that is connected between a connection point between the third switch means and the first reactor, and an interconnection point between the capacitors;
a second filter capacitor that is connected between a connection point between the fourth switch means and the second reactor, and an interconnection point between the capacitors; and
a control apparatus that controls a voltage difference between the two capacitors, wherein:
if the first and second AC power supplies operate normally, the control apparatus turns on the first switch means, the second switch means, and the fifth switch means and turns off the third switch means and the fourth switch means, so that a current flowing to the first reactor is controlled using the series body of the first switching means to perform AC/DC conversion, a high-frequency current flowing to the first reactor is absorbed using the first filter capacitor, a current flowing to the second reactor is controlled using the series body of the second switching means to perform AC/DC conversion, and a high-frequency current flowing to the second reactor is absorbed using the second filter capacitor; and
if one of the first and second AC power supplies operate abnormally, the control apparatus turns off the first switch means and the second switch means, sets a voltage of the second filter capacitor to approximately zero through switching of the series body of the second switching means, sets a current of the first reactor to approximately zero through switching of the series body of the first switching means, turns on the third switch means and the fourth switch means, turns off the fifth switch means, connects the first reactor to a connection point between the second reactor and the series body of the second switching means, and connects the first reactor to the second reactor in series, so that energy is supplied to the two capacitors using the battery and a current flowing to the first reactor is controlled using the series body of the first switching means.
With this construction, in the power conversion apparatus having the plurality of AC power supplies, when at least one of the AC power supplies operates abnormally, even in the case where loads that are respectively connected to two capacitors are unbalanced, it is possible to balance voltages of these capacitors. Also, during this operation, there is obtained an effect that it is possible to reduce losses and noises by reducing ripple currents flowing to reactors due to the opening/closing of the first switching means. Also, there is circumvented a situation where electric charges of the second filter capacitor are discharged when the fourth switch means is turned on and therefore a steep current flows to the fourth switch means and the fourth switch means is damaged. Also, the fifth switch means is turned off by setting the current of the first reactor to zero, so that there is circumvented a problem that the fifth switch means is damaged by energy accumulated in the first reactor when the fifth switch means is turned off.
According to the present invention, a third power conversion apparatus is provided with: a first AC/DC conversion means constructed by connecting a first AC power supply, a first reactor, and a series body of a first switching means in series; a second AC/DC conversion means constructed by connecting a second AC power supply, a second reactor, and a series body of a second switching means in series; two capacitors connected in series, an interconnection point of the two capacitors being connected to one end of each of the two AC power supplies, and the two capacitors receiving energy supplied by DC voltages obtained by the first and second AC/DC conversion means; loads that are respectively connected to the two capacitors; and a battery connected to the two capacitors that are connected in series,
the power conversion apparatus comprising:
a first switch means that is connected between the first AC power supply and the first reactor;
a second switch means that is connected between the second AC power supply and the second reactor;
a third switch means that is connected between a connection point between the first switch means and the first reactor, and a connection point between the second reactor and the series body of the second switching means;
a fourth switch means that is connected between a connection point between the second switch means and the second reactor, and an interconnection point between the capacitors;
a first filter capacitor that is connected between a connection point between the third switch means and the first reactor, and an interconnection point between the capacitors;
a second filter capacitor that is connected between a connection point between the fourth switch means and the second reactor, and an interconnection point between the capacitors; and
a control apparatus that controls a voltage difference between the two capacitors, wherein:
if the first and second AC power supplies operate normally, the control apparatus turns on the first switch means and the second switch means and turns off the third switch means and the fourth switch means, so that a current flowing to the first reactor is controlled using the series body of the first switching means to perform AC/DC conversion, a high-frequency current flowing to the first reactor is absorbed using the first filter capacitor, a current flowing to the second reactor is controlled using the series body of the second switching means to perform AC/DC conversion, and a high-frequency current flowing to the second reactor is absorbed using the second filter capacitor; and
if one of the first and second AC power supplies operate abnormally, the control apparatus turns off the first switch means and the second switch means, sets a voltage of the first filter capacitor to approximately zero through switching of the series body of the first switching means, sets a voltage of the second filter capacitor to approximately zero through switching of the series body of the second switching means, turns on the third switch means and the fourth switch means, connects the first reactor to a connection point between the second reactor and the series body of the second switching means, and connects the first reactor to a parallel connection body of the second reactor and the first filter capacitor in series, so that energy is supplied to the two capacitors using the battery and a current flowing to the first reactor is controlled using the series body of the first switching means.
With this construction, in the power conversion apparatus having the plurality of AC power supplies, when at least one of the AC power supplies operates abnormally, even in the case where loads that are respectively connected to two capacitors are not balanced, it is possible to balance voltages of these capacitors. Also, during this operation, there is obtained an effect that it becomes possible to reduce losses and noises by reducing ripple currents flowing to reactors due to the opening/closing of the first switching means. Also, there is circumvented a situation where electric charges of the second filter capacitor are discharged when the fourth switch means is turned on and therefore a steep current flows to the fourth switch means and the fourth switch means is damaged. Further, it is also possible to suppress unnecessary resonance between the first filter capacitor and the second reactor when the third switch means is turned on, which makes it possible to reduce losses.